System and method for assisting in the manufacture of a wind turbine blade shell

ABSTRACT

A method of manufacturing a wind turbine blade shell part is described. Fiber mats and a root end insert are laid up in a mould part in a layup procedure by use of an automated layup system. The fiber mats are laid up by use of a buffer so that the fiber mats may continuously be laid up on the mould surface, also during a cutting procedure. The root end insert is prepared in advance and mounted on a mounting plate. The root end insert is lowered onto the mould by use of the mounting plate and a lowering mechanism. After the wind turbine blade shell has been moulded, the mounting plate is removed.

This is a National Phase Application filed under 35 U.S.C. 371 as anational stage of PCT/EP2013/061242, filed May 31, 2013, the content ofwhich is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a system for automated layup of fibremats and a method of laying up fibre mats for the manufacture of partsfor a wind turbine blade, in particular the aerodynamic shell part of awind turbine blade. The present invention further relates to a method ofmanufacturing a wind turbine blade shell part made of a compositestructure comprising a fibre-reinforcement material embedded in apolymer matrix. The present invention additionally relates to a root endassembly for use in the method for manufacturing the wind turbine bladeshell. Finally, the invention also relates to a mould for manufacturinga wind turbine blade shell part.

BACKGROUND

Wind turbine blades of fibre-reinforced polymer and in particular theaerodynamic shells of wind turbine blades are usually manufactured inmoulds, where the pressure side and the suction side of the blade aremanufactured separately by arranging glass fibre mats in each of the twomould parts. Then, the two halves are glued together, often by means ofinternal flange parts. Glue is applied to the inner face of the lowerblade half before the upper blade half is lowered thereon. Additionally,one or two reinforcing profiles (beams) are often attached to the insideof the lower blade half prior to gluing to the upper blade half.

The aerodynamic shell parts are typically made by use of Vacuum AssistedResin Transfer Moulding (VARTM), where a plurality of fibre mats arearranged on top of a rigid mould parts and possibly also a core materialto provide parts having a sandwich structure. When the fibre mats havebeen stacked and overlapped so as to form the final shape of the windturbine blade shell part. Then a flexible vacuum bag is arranged on topof the fibre mats and sealed against the rigid mould part, therebyforming a mould cavity containing the fibre mats. Resin inlets andvacuum outlets are connected to the mould cavity. First the mould cavityis evacuated via the vacuum outlets so as to form an underpressure inthe mould cavity, after which a supply of liquid resin is supplied viathe resin inlets. The resin is forced into the mould cavity due to thepressure differential and impregnates the fibre material of the fibremats. When the fibre material has been fully impregnated, the resin iscured in order to form the final composite structure, i.e. the windturbine shell part.

Many of the above processes including the layout of the fibre mats areusually carried out manually.

Wind turbine blades have become increasingly longer of the years andblades having a length of more than 70 meters are now commerciallyavailable on the market. This also means that larger moulds have to beused. Due to the large size, it has become increasingly complicated tolay out the fibre mats and further to obtain proper wetting of the fibrematerial. None the less, many of the different processes are stillcarried out manually, which increases the risk of errors occurring, suchas formation of wrinkles in the fibre material or areas of insufficientwetting of the fibre material, which in turn can be detrimental to themechanical strength of the composite structure and may necessitate thatthe manufactured wind turbine blade shell part has to scrapped. Further,the cycle time for each process, i.e. laying up fibre material,impregnating the fibre material and curing the resin to form the finalproduct, all increase.

DISCLOSURE OF THE INVENTION

Accordingly, there is a need for systems and methods that will improvethe quality of the wind turbine blade shell parts (or at least decreasethe risk of errors occurring) and that can lower the cycle time of thevarious processes.

According to a first aspect, the invention provides a fibre mat layupsystem for laying up and cutting fibre mats in a mould for themanufacture of a fibre-reinforced composite part, in particular a partfor a wind turbine blade, such as an aerodynamic shell part, wherein thesystem is adapted to laying up the fibre mat as it is moved in alongitudinal direction along the mould, and wherein the systemcomprises: a first drive roller for advancing the fibre mat, a cuttingdevice for cutting the fibre mat, a first clamping device for clampingthe fibre mat, while the fibre mat is being cut by the cutting device, abuffer roller providing a buffer length for the fibre mat and beingarranged downstream of the first drive roller, the first clamping deviceand the cutting device, the buffer roller being movable so as to varythe buffer length of the fibre mat, and a second drive roller foradvancing the fibre mat and being arranged downstream of the bufferroller.

This provides for a system, where the fibre mat may continue to be laidup, while the fibre mat is being cut. This may be carried out by thefirst clamping device immobilising a first part of the fibre mat, whilethe fibre mat is being cut. The system continues to propagate along themould and laying up the fibre mat. This can be carried out, since thesecond drive roller continues to advance the fibre mat and the bufferroller position is varied so as to decrease the buffer length. Thereby,the layup cycle time will not be affected by the cutting process time.The fibre mat layup system lays up the fibre mat by moving along themould as opposed to systems utilising a gripper that pulls the fibre matalong the mould.

Accordingly, the drive rollers of the fibre mat layup system alsoadvances the fibre mat with approximately the same speed as the layupsystem is moved along the mould. Otherwise, the fibre mat would eitherbe dragged along the mould or tend to wrinkle during layout.

The cutting position of course determines the total length of the fibremat being laid out.

The drive rollers are defined as devices that may advance the fibre matsinternally in the fibre mat layup system. The drive roller may be formedby a single roller or two or more rollers engaging the fibre mat. Thedrive roller may also comprise a belt a belt and plurality of rollersrotating the belt.

According to an advantageous embodiment, the fibre mat is supplied froma fibre mat roll. The fibre mat roll is preferably moved along the mouldtogether with the fibre mat layup system. However, in principle, thefibre mat roll may also be stationary.

According to another advantageous embodiment, the system furthercomprises a draping device arranged downstream of the second driveroller. The draping device ensures that wrinkles in the laid up fibremats are reduced and aligns the fibres in the correct orientation. Thisis particular relevant, if the advancement speed from the drive rollersis not exactly aligned with the movement speed of the fibre mat layupsystem along the mould. In one embodiment, the draping device comprisesone or more rollers, such as a compression roller. Alternative or inaddition thereto, the draping device may draping device comprises anumber of brushes or pads. The brushes may for instance be flexiblerubber pads that are dragged along with the fibre mat layup system, thusdraping the fibres as they are moved along the fibre layers.

According to one advantageous embodiment, the cutting device is anultrasonic knife. The cutting device may also be a rotary cutter. Inprinciple any cutting device suitable for cutting fibre mats may beused.

In another advantageous embodiment, the system is adapted to lay outfibre mats having a width of at least 20 cm. In other words, the fibremat has a width of at least 20 cm. Alternatively, the fibre mat has awidth of at least 30 cm, or at least 40 cm, or at least 50 cm. Thesystem may also be adapted to lay up fibre mats having a width ofbetween 20 cm and 80 cm. Thus, the fibre mats may have a maximum widthof 80 cm.

The fibre mats may comprise any type of reinforcement fibres suitablefor reinforcing large composite structures, such as glass fibres, carbonfibres or aramid fibres. The fibre mats may comprise unidirectionalfibres, biaxial fibres, triaxial fibres or randomly oriented fibres.

In yet another advantageous embodiment, the system is adapted to lay upfibre mats with a speed of between 25 m/minute and 100 m/minute.Alternatively, the system is adapted to lay up fibre mats with a speedof between 50 m/minute and 100 m/minute, e.g. around 72 m/minutes (or inother words 1.2 m/s).

According to one embodiment, the system is adapted slow down itsmovement speed along the movement during cutting of the fibre mat.

In one advantageous embodiment, the first drive roller is arrangedsubstantially vertical above the second drive roller, and preferablyalso substantially vertical above the first clamping device. Thisprovides for a simple solution of advancing the fibre mat from the firstdrive roller to the second drive roller, after the fibre mat has beencut. The buffer roller may advantageously be arranged so as to bemovable in a direction substantially transverse to the direction betweenthe first drive roller and the second drive roller. Thus, the bufferroller may for instance be movable in a substantially horizontaldirection. This provides for a simple solution of providing and varyingthe buffer length of the fibre mat.

According to a particular advantageous embodiment, the buffer roller isresiliently biased. Thus, the buffer may biased with a bias force thatexceeds the pulling force from the fibre mat, when the first clampingdevice is disengaged. Once the first clamping device is engaged, thesecond drive means will continue to advance the fibre mat, which in turnwill apply a pulling force to the buffer roller. Since the pulling forceexceeds that of the bias force, the buffer roller will be moved an inturn decrease the buffer length. The buffer roller may for instance bebiased by use of gas pressure or by use of a spring.

In one embodiment, the buffer roller may be locked in a disengagedposition, where the buffer length is minimised. The buffer length mayfor instance be zero, when the buffer roller is locked in the disengagedposition. The buffer roller may be locked in a position, where the cutfibre end may be advanced passed the buffer roller to as to be advancedto a degree where the fibre mat again engages the second drive roller.This can be carried out by having suitable means for guiding the fibremat past the buffer roller, or e.g. by having the first drive means andthe second drive means being arranged substantially above each other.Afterwards, the buffer roller may be moved to the biased position againto provide a new buffer length.

The first clamping device may comprise clamping rollers. In oneembodiment, the fibre mat layup system is provided with sensors thatused to monitor the tension of the fibre mat. This may in turn be usedto control the bias force applied to the buffer roller.

According to a first additional aspect, the invention also provides amethod of manufacturing a composite part, in particular a part for awind turbine blade, such as an aerodynamic shell part, wherein fibremats are laid up in a mould part in a layup procedure by use of anautomated fibre mat layup system, wherein the layup procedure comprisesthe steps of: a) delivering a supply of one or more fibre mats to thefibre mat layup system, b) laying up a first length of a fibre mat ontoa surface of the mould along a first longitudinal part of the mould bymoving the fibre mat layup system in a longitudinal direction of themould, c) clamping a first part of the fibre mat, d) cutting the fibremat at a cutting position, and while step d) is carried out e) laying upa second length of the fibre mat by continuing to move the fibre matlayup system along the mould, while a buffer length arranged downstreamof the first part of the fibre mat is being reduced, and f) repeatingsteps a)-e) to define a plurality of laid out fibre mats defining thecomposite part.

Thus, the method involves the continuing steps of laying up and cuttingfibre mats, which are arranged and overlapped so as to cover theintended part of the mould and stacked until a desired laminatethickness is obtained. The method allows the fibre mat to be continuedto be laid out during the cutting step, thereby not adversely affectingthe layup cycle time. The fibre mat layup system may be moved to a newstart position for laying out the next fibre mat length, while the nextpiece of fibre mat is delivered to the fibre mat layup system.

In one advantageous embodiment, the buffer length in step f) is reducedby varying the position of a buffer roller, the buffer roller providinga buffer length for the fibre mat.

In another advantageous embodiment, delivery of the one or more fibremats in step a) involves advancing the one or more fibre mats to aposition, where they extend from a first drive roller to the bufferroller arranged downstream of the first drive roller and further onto asecond drive roller arranged downstream of the buffer roller. Thisensures that the fibre mat may still be advanced, once it has been cutin step d).

In yet another advantageous embodiment, the delivery is carried outwhile the buffer roller is in a retracted position, and wherein thefirst drive roller advances the fibre mat until it engages the seconddrive roller. Thus, the fibre mat may be advanced passed the roller. Thebuffer roller may subsequently be moved to an engaged position, whereinthe drive roller provides the buffer length of the fibre mat.

According to an advantageous embodiment, the fibre mat layup systemafter step e) is moved to a new start position for laying out a fibremat, while a subsequent delivery of a supply of one or more fibre matsto the fibre mat layup system fibre mat is carried out.

In one embodiment, the fibre mat layup system during step b) is movedalong the mould at a first speed, and the fibre mat layup system is instep e) is moved along the mould at a second speed being lower than thefirst speed.

In one embodiment, sensors are used to monitor the tension of the fibremat. This may in turn be used to control the bias force applied to thebuffer roller.

In one embodiment, the fibre mat layup system is turned between layingout a fibre fibre mat and a second fibre mat. Thus, the first fibre matis laid out in the longitudinal direction of the mould, whereas the nextis laid out in the opposite direction. Alternatively, the fibre matlayup system is moved back to start of layup of the next fibre mat andlaid out in the same direction.

According to a second aspect, the invention provides a method ofmanufacturing a wind turbine blade shell part made of a compositestructure comprising a fibre-reinforcement material embedded in apolymer matrix, wherein the method comprises the steps of: a) arrangingone or more outer fibre layers on a mould surface, the one or more outerfibre layers defining an outer surface of the wind turbine blade shellpart, b) mounting a plurality of fastening devices on a mounting plateso as to form a root end assembly, c) arranging the root end assembly ontop of the one or more outer fibre layers at a root end section of themould, d) arranging one or more inner fibre layers on top of the rootend assembly, e) supplying a polymer to the outer and inner fibrelayers, f) allowing the polymer to cure so as to form the compositestructure, and removing the mounting plate.

This provides for a method, wherein the plurality of fastening devicescan be arranged in the mould in a single step instead of the prior artmethod, where the fastening devices are arranged separately. The priorart method of separately arranging the bushings on the mould is atedious procedure and is proned to error. By use of the method accordingto the invention, the fastening devices or bushings may be arranged onthe mounting plate, and all the bushings may then be arranged correctlyon the fibre layers on the mould. This also speeds up the manufacturingprocess, since all the fastening members may be arranged on the fibrematerial in one step, and since fibre layup in the mould and thepreparation of root end assembly may be prepared in parallel.

The fastening members are in the final composite structure of the shellpart embedded between the outer fibre layer(s) and the inner fibrelayer(s). The fastening members are accessible from the root end of theshell part so that the wind turbine blade may be mounted to the hub of awind turbine.

The mounting plate may remain on the root end of the wind turbine bladeshell part after the manufacture of the shell part and only be removedprior to instalment on the wind turbine hub. Thereby, the rigid mountingplate ensures that the root end of the blade does not deform duringstorage. In manufacturing methods, where the blade shell is manufacturedvia two or more blade shell parts, such as the suction side shell partand the pressure side shell part, the mounting plate may also remainattached to the blade shell parts during the step, where the blade shellparts are glued to each other.

When the mounting plate of the root end assembly has been removed, theremaining part constitutes a root end insert.

According to a preferred embodiment, the fastening members are bushings.The bushings are arranged so that the opening of the bushings areaccessible from the root end of the blade shell so that the final windturbine blade may be mounted to the hub of a wind turbine by use of staybolts inserted into the openings of the bushings.

According to an advantageous embodiment, the bushings are mounted on themounting plate by use of stay bolts. The mounting plate may be providedwith openings for the stay bolt to be inserted through, so that thebushings are mounted on a first side of the mounting plate, and the staybolts are inserted through said openings and attached to the bushingfrom a second, opposite side of the mounting plate. The mounting platemay be removed from the root end by first demounting the stay bolts andthen removing the mounting plate from the root end of the blade shellpart.

According to another advantageous embodiment, the mounting plate isprovided with guiding recesses for insertion of one end of the fasteningmembers. This ensures correct alignment and orientation of the fasteningmembers.

In yet another advantageous embodiment, the preparation of the root endassembly further comprises the step of mounting inserts between thefastening members. The inserts may for instance be retaining inserts,such as butterfly wedges, which retain the fastening members and furtherensures that the fastening members are arranged with the correct mutualspacing. In practice, the fastening members and the inserts may bearranged on the root end assembly by alternately arranging the fasteningmember and the inserts, preferably along a circular or semi-circularpath on the mounting plate.

The inserts may advantageously be made of a fibre-reinforced compositestructure, e.g. a fibre pultrusion comprising pultruded glass fibres orcarbon fibres.

In one embodiment, fibre material is wrapped around the fasteningmembers. The fibre material may advantageously be non-woven fibrematerial, such as glass wool.

The fastening members are typically made of a metal, such as cast ironor stainless steel, and by wrapping fibre material, e.g. glass fibres,around the fastening members, it is ensured that the fastening membersare properly bonded to the inner and outer fibre layers.

In one advantageous embodiment, a wedge is arranged in longitudinalextension of the fastening member. The wedge may for instance be made offoamed polymer or balsawood. The wedge is arranged so that it has thethickest part proximal to the end of the fastening member, and the thinpart distal to the end of the fastening member. This ensures that theroot end assembly has a gradual transition to the outer and inner fibrelayers, in turn ensuring that the blade root does not have a steep ordiscontinuous stiffness transition.

The wedge may be wrapped in the fibre material together with thefastening member so that the two parts may be arranged on the mountingplate together. The wedge may also in principle be integrally formedwith the fastening member.

In another advantageous embodiment, the inserts comprises a tapered partor wedge part. The tapered part of the insert may preferably be alignedwith the wedge arranged in longitudinal extension of the fasteningmember. Thereby, the two parts together ensure a gradual stiffnesstransition in the composite structure of the shell part.

A fibre material may advantageously be weaved between the wedges of thefastening members and the wedge part of the inserts. This can be done byweaving the fibre material under the butterfly wedges and over thefastening member wedges or vice versa. The fibre material may forinstance be triaxial glass fibre mats.

In yet another advantageous embodiment, a fibre layer, such as a fibremat, is wrapped around the plurality of fastening members and theoptional inserts prior to the root end assembly being arranged in themould. The fibre layer may for instance be a triaxial fibre matcomprising glass fibres.

Further, a number of fibre bands may be arranged on top of the wedges inorder to a proper alignment of the end parts of the edges and a properdraping of the fibre material, thus ensuring a proper transition to theinner and outer fibre layers without wrinkles forming in the laminate.

The outer fibre layer(s) may advantageously comprise biaxial fibre mats.The inner fibre layer(s) may advantageously comprises triaxial fibremats.

According to the second aspect, the invention also provides a root endassembly comprising a mounting plate comprising a first side and asecond side, and a plurality of fastening members, such as bushing,mounted to the first side of the mounting plate so that the fasteningmembers extend substantially normal to first side of the mounting plate,wherein the mounting plate is adapted to be removed, when the root endassembly has been mounted in a wind turbine blade shell part.

Thus, it is seen that the root end assembly corresponds to theintermediate product obtainable by step b) of the method according tothe invention.

According to an advantageous embodiment, the assembly further comprisesa number of inserts arranged between the fastening members. Thereby, thefastening members and the inserts may together form a root end insertthat is embedded in the entire cross-section, thus forming a circularinsert in the finished wind turbine blade shell. The inserts and thefastening members preferably comprise lateral sides that abut eachother.

The fastening members may advantageously be made of metal, such as castiron or stainless steel.

According to an advantageous embodiment, the assembly further comprisewedges arranged in longitudinal extension of the fastening members,alternatively the wedges being provided with a tapering part proximal tothe mounting plate. Similarly, the inserts may comprise a tapering partproximal to the mounting plate. The wedges or tapering parts may thusprovide for a gradual stiffness transition in the longitudinal directionof the finished wind turbine blade shell.

According to another advantageous embodiment, the mounting plate on thefirst side comprises recesses or notches, and a proximal end of thefastening members are arranged in said recesses or notches. The recessesmay assist in ensuring that the fastening members are arranged correctlyon the mounting plate, e.g. ensuring that the fastening members extendalong a normal to a plane of the mounting plate. The recesses arepreferably disposed along a circular path or semi-circular path on themounting plate so that the fastening members are arranged along acircular cross section of the wind turbine blade shell part.

According to yet another advantageous embodiment, the mounting platefurther comprises a number of holes, wherein the fastening members areattached to the mounting plate by stay bolts that have been insertedfrom the second side of the mounting plate and through the holes. Thus,the holes are preferably also disposed along a circular path.Preferably, the holes are aligned with the recesses on the first side ofthe mounting plate.

In one embodiment, the mounting plate is provided with attachmentdevices for attaching the mounting plate to the lowering device. Theattachment devices may for instance be pins that may mate or rest onhooks provided on the lowering device.

According to a third aspect, the invention provides a mould formanufacturing a wind turbine blade shell part, the mould being providedwith a moulding surface that defines the outer shape of the wind turbineshell part, wherein the mould has a longitudinal direction and comprisesa root end mould part at a longitudinal end thereof, and wherein themould is provided with a lowering mechanism, which is adapted to carryand lower a root end insert onto the moulding surface of the mould.

This ensures that a root end insert that has been separately preparedmay be lowered and arranged very precisely onto the moulding surface.Further, the lowering process can to a high degree be carried outwithout human involvement. Hitherto, root end inserts have been mountedmanually, and the quality of the process therefore heavily relied on theskills of the operator. By using an automatic lowering mechanism it isensured that the root end insert is lowered into the mould every timesuch a root end insert is being mounted. Safety is also increased, asthere is no manual operation for fixing the root plate, while the rootend insert is being carried by a carrying device, such as a crane.

In practice, the root end insert may be arranged on a mounting plate,the mounting plate and the root end insert together forming a root endassembly. The root end insert is then arranged in the mould by providingthe root end assembly on the lowering device and lowering it into themould. The mounting plate may then later, e.g. after moulding, beremoved.

The lowering mechanism may advantageously be attached to the mould,preferably on the sides of the mould. This ensures that the loweringmechanism is always aligned in the same way relative to the mould, inturn ensuring that the root end insert is lowered onto the mouldingsurface in the same way every time.

According to an advantageous embodiment, the lowering mechanism isadapted to lower the root end insert in a two-step motion, where theroot end insert in a first motion step is lowered onto the mouldingsurface while the root end insert is angled upwards in the longitudinaldirection until a first end of the root end insert contacts a part ofthe moulding surface at the root end, and where the root end insert in asecond motion step is tilted until the root end insert rests on themoulding surface. Thereby, the lowering mechanism may lower the root endinsert onto the moulding surface without wrinkling or otherwisedistorting fibre material, such as fibre mats, that have been laid up onthe moulding surface prior to arranging the root end insert in themould.

The root end insert is in the second motion step rotated substantiallyabout the first end of the root end insert or the part that after thefirst motion step contacts the part of the moulding surface at the rootend.

According to an advantageous embodiment, the lowering mechanismcomprises a frame for carrying the root end insert and a driving meansfor lowering the frame together with root end insert. This provides fora simple solution, where the root end insert or root end assembly may bearranged on the frame, and where the driving means facilitate thelowering motion, where the root end insert is arranged on the mouldingsurface.

According to another advantageous embodiment, the lowering mechanismcomprises at least a pair of guiding pins or rollers and mating guidingslots provided on the frame. The mating connection between the guidingpins and the guiding slots may thus ensure that the root end insertfollows the correct motion, when it is lowered onto the mouldingsurface.

The guiding slots may advantageously comprise a front guiding slot and arear guiding slot, wherein the slots are shaped so that rear guide inthe first motion lowers a rear part of the frame faster than the a frontguiding slot lowers a front part of the frame. Thereby the frame will beboth lowered and tilted during the first motion step, thus tilting theroot end insert upwards as seen in the longitudinal direction of themould.

In one advantageous embodiment, the slots are shaped so that the frontguide in the second motion lowers the front part of the frame fasterthan the rear guiding slot lowers the rear part of the frame. Thus, theguiding slots are shaped so as to provide the rotating motion of thesecond motion step.

In another advantageous embodiment, the driving means comprises atelescopic piston cylinder, such as a hydraulic or pneumatic piston.This provides a particular simple solution for moving the frame and thuslower the root end insert onto the moulding surface.

In yet another advantageous embodiment, the frame is provided carryingmeans for carrying the root end insert. This provides a simple solutionfor arranging and carrying the root end insert on the frame of thelowering device. The carrying means may for instance be hooks that areadapted to receive pins or rods from the root end insert. The root endinsert or more precisely the mounting plate of the root end assembly maythus rest on the hooks.

According to the third aspect, the invention also provides a method ofmanufacturing a wind turbine blade shell part, wherein the wind turbineblade shell part is manufactured as a composite structure comprising afibre-reinforcement material embedded in a polymer matrix, and whereinthe wind turbine blade shell part is provided with a root end insertthat, when manufactured, is accessible from a root end of the windturbine shell part, and wherein the wind turbine blade shell part ismanufactured in a mould provided with a moulding surface that defined anouter shape of the wind turbine blade shell part, wherein the methodcomprises the steps of: a) arranging the root end insert on a loweringdevice of the mould, and b) lowering the root end insert onto themoulding surface of the mould via the lowering device.

This ensures that a root end insert that has been separately preparedmay be lowered and arranged very precisely onto the moulding surface.Further, the lowering process can to a high degree be carried outwithout human involvement. By using an automatic lowering mechanism itis ensured that the root end insert is lowered into the mould every timesuch a root end insert is being mounted. Safety is also increased, asthere is no manual operation for fixing the root plate, while the rootend insert is being carried by a carrying device, such as a crane.

The lowering mechanism is advantageously arranged on the mould, e.g. onthe sides of the mould.

In an advantageous embodiment, step b) is carried out in two motionssteps, wherein b1) the root end insert in a first motion step is loweredonto the moulding surface while the root end insert is angled upwards inthe longitudinal direction until a first end of the root end insertcontacts a part of the moulding surface at the root end, and b2) theroot end insert in a second motion step is tilted until the root endinsert rests on the moulding surface. Thereby, the root end insert maybe lowered onto the moulding surface without wrinkling or otherwisedistorting fibre material, such as fibre mats, that have been laid up onthe moulding surface prior to arranging the root end insert in themould. The root end insert is in the second motion step rotatedsubstantially about the first end of the root end insert or the partthat after the first motion step contacts the part of the mouldingsurface at the root end.

According to a particular advantageous embodiment, the root end insertprior to step a) is arranged on a mounting plate, and the root endinsert is arranged on the lowering mechanism via the mounting plate.

The mounting plate together with the root end insert form a root endassembly.

The root end insert may comprise a plurality of fastening members, suchas bushings. The fastening members are accessible from the end of thewind turbine blade shell so that the fastening members in the final windturbine blade can be used to mount the root end of the wind turbineblade to the hub of a wind turbine. The root end insert furthercomprises a number of inserts arranged between fastening members.

As previously mentioned, the lowering mechanism comprises a frame forcarrying the root end insert and a drive device for lowering the frametogether with root end insert. The frame and the root end insert may belowered onto the moulding surface of the mould via guiding slots andguiding pins or rollers.

According to an advantageous embodiment, the method prior to step a)comprises the step of arranging one or more outer fibre layers on themoulding surface, the one or more outer fibre layers defining an outersurface of the wind turbine blade shell part. According to anotheradvantageous embodiment, the method additionally comprises the step ofarranging one or more inner fibre layers on top of the root end insert.Thereby, the root end insert is sandwiched between the inner fibrelayer(s) and outer fibre layer(s).

According to yet another advantageous embodiment, the method after stepb) comprises the steps of supplying a polymer to the outer and innerfibre layers, and allowing the polymer to cure so as to form thecomposite structure. The root end insert is thus embedded in thecomposite structure, thus providing a strong attachment part formounting the final wind turbine blade to the hub of a wind turbine.

In methods where the root end insert is arranged on the moulding surfaceby use of a mounting plate, the mounting plate may be removed after thepolymer has cured.

The various embodiments of the three aspects may be combined in any way.For instance may the root end assembly of the second aspect be arrangedon the lowering mechanism of the third aspect. This can for instance becarried out by the root end insert being arranged on a mounting plate,the root end insert and the mounting plate together forming the root endassembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in details below with reference to anembodiment shown in the drawings, in which

FIG. 1 shows a schematic view of a wind turbine provided with three windturbine blades, at least one of these blades having a blade shell halfbeing produced according to the method according to the invention

FIG. 2 shows a schematic view of a mould used for manufacturing a windturbine blade shell part

FIG. 3 shows cross-sectional view of the mould a system according to theinvention for automated layup of fibre mats,

FIGS. 4-10 show side views of the system according to the inventionduring layup of fibre mats on the mould,

FIG. 11 shows a top view of a mould surface of the mould with outerfibre layers arranged on the mould surface,

FIGS. 12 and 13 show schematic views of a mounting plate according tothe invention for mounting a root end insert,

FIG. 14 shows a profile view of a bushing and wedge of the root endinsert,

FIG. 15 shows a top view of wedges and inserts of the root end insert,

FIG. 16 shows a cross-section of the root end insert,

FIGS. 17-19 show schematic side views of the mould provided with alowering mechanism according to the invention,

FIG. 20 shows a top view of a mould surface of the mould with innerfibre layers arranged on top of the root end insert, and

FIG. 21 shows a cross-section of the layup in a root section of themould.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a conventional modern upwind wind turbine 2 accordingto the so-called “Danish concept” with a tower 4, a nacelle 6 and arotor with a substantially horizontal rotor shaft. The rotor includes ahub 8 and three blades 10 extending radially from the hub 8, each havinga blade root 16 nearest the hub and a blade tip 14 furthest from the hub8. The rotor has a radius denoted R.

The wind turbine blades 10 are manufactured as fibre-reinforcedcomposite structures comprising a fibre-reinforcement material embeddedin a polymer matrix. The individual blades 10 comprise an aerodynamicshell, and the suction side and the pressure side of the aerodynamicshell are often manufactured as separate parts in moulds 20 as shown inFIG. 2. The blade shell parts 11 are manufactured separately byarranging the fibre-reinforcement material and typically also sandwichcore material, such as foamed polymer or balsawood, on a mould surface22 of the mould. The fibre reinforcement material is laid out asseparate fibre mats 24 that are stacked overlapping on the mould surface22. The load bearing structure of the blade 10 may be manufactured as aspar cap integrated in the blade shell, also called a main laminate,with shear webs arranged between the spar caps of the pressure sideshell part and the suction side shell part. Alternatively, the loadbearing structure may be formed as a spar or a beam, and the aerodynamicshell is adhered to the load bearing structure. The two blade shellparts are also glued to each other, e.g. by use of internal flangeparts. The fibre mats 24 may be laid up manually on the mould surface 22or by use of a fibre mat layup system, in which case the fibre mats 24may be laid up automatically or semiautomatically.

FIG. 3 shows a cross-section of the mould 20 in a manufacturing setup,where a fibre mat layup system 30 is utilised to lay up the fibre mats24. The fibre mat layup system 30 is carried on a frame 63 and the fibremats 24 are laid up by the fibre mat layup system 30 being moved alongthe mould 20 by use of a cart or portal 60. The fibre mat material isdelivered to the fibre mat layup system 30 from a fibre mat roll 50 thatalso is carried on the frame and thus is moved together with the fibremat layup system 30 along the mould. The portal 60 comprises a firsttelescopic portion 61 and a second telescopic portion 62 so that thetransverse position and the height of the frame 63 and thereby also thefibre mat layup system 30 may be varied. Further, the frame may berotated about a pivot 64 m, whereby the layup angle of the fibre mats 24may be varied. Thereby, the position and angle of the fibre mat layupsystem 30 can be varied in order to lay out the fibre mats at thedesired position and to accommodate the shape of the mould surface 22.The position and angle of the fibre mat layup system 30 may bepreprogrammed so that the fibre mats 24 may be cut and laid up in anautomated or semiautomated process. The portal may for instance be movedacross the factory floor 66 by use of rails or wheels 65.

FIGS. 4-10 show side views of the fibre mat layup system 30 during alayup and cutting procedure according to the invention. As shown in FIG.4, the fibre mat 24 is supplied to the fibre mat layup system 30 fromthe fibre mat roll 50. The fibre mat layup system 30 comprises a firstdrive roller 32 that advances the fibre mat 24 within the fibre matlayup system 30. A cutting device 34 for cutting the fibre mat 24 isarranged downstream of the first drive roller 32. The cutting device 34may for instance be a sonic knife or a rotary cutter. A buffer roller 38is arranged downstream of the cutting device 34 and provides for abuffer length 39 of the fibre mat. The buffer roller 38 is arranged inslots 44 so that the buffer roller 38 may be moved in a substantiallyhorizontal direction so that the buffer length 39 may be varied, and thebuffer roller is resiliently biased, e.g. by air pressure to provide thebuffer length 39. A first clamping device 36 is arranged between thecutting device 34 and the buffer roller 38.

A second drive roller 40 for advancing the fibre mat 24 within the fibremat layup system 30 is arranged downstream of the buffer roller 38 andbuffer length. The first drive roller 32 and the second drive roller 40are arranged substantially vertically above each other. Thus, the bufferroller position is variable in a position substantially transverse tothe general direction of fibre mat advancement, which in turn provides asimple solution for varying the buffer length 39.

The speed of the first and the second drive rollers 32, 40 is generallyaligned with the propagation speed of the fibre mat layup system 30along the mould. This ensures that the fibre mats 24 can be arranged onthe mould surface 22 without being dragged along the mould surface andwithout the fibre mats wrinkling. The fibre mat layup system 30 furthercomprises a tray 42 for arranging the fibre mats 24 on top of the mouldsurface 22. The tray may be angled so that the tension of the fibre matis relieved as it is arranged on top of the mould surface 22. The fibremat layup system 30 further comprises a draping device 48. The drapingdevice 48 may for instance comprise one or more compression rollers.Alternative or in addition thereto, the draping device may drapingdevice comprises a number of brushes or pads. The brushes may forinstance be flexible rubber pads that are dragged along with the fibremat layup system, thus draping the fibres as they are moved along thefibre layers.

The fibre mat 24 needs to be cut in order to provide the correct fibremat length. The layout and cutting method according to the invention isthus carried out in two layup steps. In the first layup step, the fibremat layup system 30 lays up a first length of the fibre mat onto thesurface, in a sequence, where the fibre mat layup system 30 continues toadvance the fibre mat 24 within the system and propagates along themould. During the layup of the first length, the first drive roller andthe second drive roller 32, 40 continues to advance the fibre length,and the pulling forces thus applied to the buffer roller 38 is lowerthan the biasing of the roller. Thereby, the buffer roller 38 is keptstationary so as to provide the full buffer length 39.

Once the fibre mat has been laid up to the first length, the secondlayup step commences. The first clamping device 36 clamps the fibre mat,thereby immobilising a part of the fibre mat, and the cutting device 34is activated and cuts the fibre mat as shown in FIG. 5. The first drivemeans 32 may also be adapted to clamp the fibre mat in order to keep thefibre mat taut during the cutting procedure. Similarly, the firstclamping device 36 may also be adapted to function as a drive roller,when the fibre mat is advanced internally in the fibre mat layup system30.

The fibre mat layup system continues to lay up a second length of thefibre mat 24 during the cutting procedure. The second length correspondsto the length of the fibre mat within the system 30 from the cuttingdevice 34 to the layup point at the tray 42 at the time of cutting.Thus, the total length of the fibre mat laid up corresponds to the firstlength plus the second length. During the cutting procedure, the seconddrive roller 40 continues to advance the fibre mat. Since the clampingdevice 36 still clamps the end of the cut fibre mat, the fibre mat willbegin to apply a pulling force to the buffer roller 38 which is largerthan the bias. Accordingly, the buffer roller begins to move along theslots 44, thereby reducing the buffer length 39. This continues untilthe buffer roller 38 is retracted to a storage or retracted position 46,in which the buffer length 39 is minimised as shown in FIG. 6.

Then the clamping device 36 disengages the fibre mat so that the end ofthe fibre mat is pulled past the buffer roller as shown in FIG. 7, whilethe fibre mat layup system 30 continues to move along the mould and layup the fibre mat on the mould surface 22 as shown in FIG. 9. The firstdrive roller 32 then starts to advance new fibre mat material from thefibre mat roll 50. The new fibre mat material is guided from the firstdrive roller 32 to the second drive roller 40. Since the buffer roller38 is stored in the retracted position 46, the fibre mat material may beadvanced past the buffer roller as shown in FIG. 9. When the new fibremat material engages the second drive roller 40, the buffer roller maybe engaged again so that the buffer length 39 may again be provided tothe system by bias force moving the buffer roller along the slots 44 asshown in FIG. 10. The advancement of the fibre mat and the reengagementof the buffer roller 38 may be carried out while the fibre mat layupsystem is moved to the start position for the next fibre mat 24 to belaid up.

Overall, the fibre mat layup system 30 and the layup procedure accordingto the invention provide a system and method, where the layup cycle timeis only minimally affected by the cutting process time.

The system is particularly suited for layup of fibre mats having a widthof 20-80 cm. The fibre mats may comprise unidirectional, biaxial,triaxial or randomly oriented fibres. The reinforcement fibres arepreferably glass fibres or carbon fibres. The layup of the first lengthof fibre mats may be carried out at a first movement speed, e.g. around72 m/min. The layup of the second length of fibre mats, i.e. the layupduring the cutting procedure, may be carried out at a lower speed. Thespeed may also be gradually reduced during the layup of the secondlength of the fibre mat.

In the following, the preparation and layup of the root part of the windturbine blade shell will be described. As shown in FIG. 11, the layupprocedure starts by arranging one or more outer fibre layers 68 on themould surface 22 of the mould. The outer fibre layers 68 advantageouslycomprise biaxial fibre layers, e.g. with the fibres oriented −45 and 45degrees compared to the longitudinal direction of the mould. The biaxialfibre layers provide a strong mechanical bonding to fastening membersprovided at the root end. The fastening members are in the finalproduct, i.e. the wind turbine blade, used for mounting the root end ofthe blade to a wind turbine hub. The biaxial fibres provide strengthboth in the longitudinal direction and the transverse direction of theblade and thus help to ensure that the fastening members are not pulledout from the wind turbine blade root.

FIGS. 12 and 13 show a mounting plate 70 that is used to prepare a rootend insert comprising a number of fastening members in form of bushings74 and retaining inserts in form of butterfly wedges 76 arranged betweenthe bushings 74. The mounting plate 70 together with the root end insertform a root end assembly. The mounting plate 70 may be used forarranging the root end insert on the mould surface 22 of the mould 20and may be removed afterwards and at least prior to instalment of theblade on a wind turbine hub.

The mounting plate 70 comprises a first side 77 and a second side 79.The mounting plate 70 is provided with a plurality of recesses 71provided on the first side 77 of the mounting plate 70 and a pluralityof through-going bores 72 or holes. The bores 72 are centrally alignedwith the recesses 71. In FIGS. 12 and 13 only a few recesses 71 andbores 72 are shown. However, in practice they are arranged equidistantlyalong an entire semi-circle of the mounting plate 70.

The bushings 74 are mounted in the recesses 71 of the mounting plate 70by inserting ends of the bushings 74 in the recesses. The bushings 74are provided with central bores having inner threads 75. The bushings 74may thus be retained in the recesses by inserting stay bolts 78 from thesecond side of the mounting plate 70 and through the bores 72 of themounting plate 70. The bushings will then extend from the first side 77of the mounting plate and be oriented substantially normal to a plane ofthe mounting plate 70.

In practice, the root end insert may be prepared by first mounting afirst bushing 74 on the mounting plat and then arranging a first insert76 next to and abutting the first bushing. Afterwards a second bushing74 is arranged next to the first insert 76 and a second insert 76 nextto the second bushing 74. This procedure is then continued untilbushings 74 and inserts 76 are arranged along the entire semi-circle onthe mounting plate, e.g. by arranging bushings 74 and inserts 76 fromleft to right as illustrated in FIG. 12. The inserts 76 need not bearranged in recesses on the first side 77 of the mounting plate, but maybe retained between the bushings 74 due to the butterfly shape of theinserts 76.

The mounting plate 70 is provided with a number of protrusions 73, suchas pins or rods, which extend from the side of the mounting plate 70.These protrusions 73 may used as connecting parts for providing a matingconnection to corresponding parts on a frame of a lowering mechanism forarranging the root end insert on the surface 22 of the mould 20.

As shown in FIG. 14, wedges 80 are arranged in longitudinal extension ofthe bushings 74. The wedges may for instance be made of foamed polymeror balsawood, whereas the bushings are made of for instance cast iron orstainless steel. The wedges 80 are arranged so that the thick part ofthe wedge 80 is arranged proximal to the bushing 74, and the thin,tapered part is arranged proximal to the bushing. This ensures that thefastening member has a gradual transition to the surrounding fibrelayers of the final blade shell part, thereby ensuring that the bladeroot does not have a steep or discontinuous stiffness transition

A fibre layer 81 may be wrapped around a bushing 74 and a wedge 80.Advantageously, the fibre layer is relatively thin band that is wrappedin a helix shape around the two parts. Thereby, the fibre layer 81,bushing 74 and wedge can be mounted together on the mounting plate 70.The fibre layer 81 may advantageously comprise non-woven fibres orrandomly oriented fibres, such as for instance glass wool. Thisfacilitates a relative strong bonding in the polymer matrix after thelater infusion and curing of the polymer.

The inserts 76 preferably also has a profile that corresponds to theprofile of bushings 74 and the wedges 80. In other words, the inserts 76preferably comprises a tapering part or wedge part at a proximal endthereof. The tapering part is advantageously integrally formed with theinsert 76. The inserts 76 may advantageously be made of afibre-reinforced composite structure, e.g. a fibre pultrusion comprisingpultruded glass fibres or carbon fibres.

As shown in FIG. 15 the tapering part or wedge part of the inserts 76may be aligned with the wedges 81 arranged in longitudinal extension ofthe bushings 74. This may be carried out by weaving a fibre band underthe tapering part of the inserts and over the wedges 81 of the fasteningmembers or vice versa.

Afterwards, an additional fibre layer 83 may be tightly wrapped anddraped around the bushings 74, wedges 80 and inserts 76 such that theroot end insert has a cross-section as shown in FIG. 16. The additionalfibre layer 83 may for instance be a triaxial fibre layer comprisingreinforcement fibres oriented −45 degrees, 0 degrees and 45 degreescompared to the longitudinal direction of the blade shell and mould.This provides strength in both the longitudinal direction and thetransverse direction of the blade shell and increases the pull-outstrength of the bushings 74. Additionally, fibre bands (not shown) maybe wrapped around the additional fibre layers 83 near the tapering partsof the wedges 81 and inserts 76 so as to ensure a smooth transition tothe surrounding fibre layers in the layup.

The root end insert has now been prepared and is ready to be arranged ontop of the outer fibre layers 68. This may be carried out as shown inFIGS. 17-19 by arranging the mounting plate 70 with the mounted root endinsert (not shown) on a lowering mechanism 85 that may lower and arrangethe root end insert on the mould surface 22 of the mould 20.

The lowering mechanism 85 may advantageously be attached to sides of themould 20. The lowering mechanism 85 comprises a frame 86, which isprovided with carrying means in form of hooks 92 that may matinglyengage the protrusions 73 of the mounting plate 70 such that themounting plate is connected to or resting on the frame 86.

The frame 86 comprises a front guiding slot 89 and a rear guiding slot90, which engage a front guiding roller 87 and a rear guiding roller 88,respectively. The lowering mechanism further comprises a driving meansin form of a telescopic piston cylinder 91 that is connected between astationary part of the lowering mechanism 85 and the frame 86. Thetelescopic piston cylinder 91 may advantageously be hingedly connectedto the stationary part and the frame 86. The guiding slots 89, 90 areshaped so that the frame 86 and therefore also the mounting plate 70with the root end insert are moved according to a desired motion.

FIG. 17 shows the lowering mechanism 85 in the mounting position, wherethe mounting plate 70 together with the root end insert are arranged onthe frame 86 of the lowering mechanism 85. The mounting plate 70 ismounted on the frame 86 in a substantially vertical orientation.

When the telescopic piston cylinder 91 begins to retract the piston, theframe 86 is moved on the guiding rollers 87, 88 via the guiding slots89, 90. As seen, the guiding slots each comprise a horizontal slot partand an angled slot part. The horizontal slot part of the front guidingslot 89 is longer than the horizontal slot part of the rear guiding slot90, and the angled part of the front guiding 89 slot is angled morecompared to a horizontal plane than the angled part of the rear guidingslot 90. Thereby, the frame 86 will in a first motion (from FIG. 17 toFIG. 18) be lowered down towards the moulding surface 22 of the mould,while the frame 86 and mounting plate 70 are tilted so that the root endinsert is angled upwards in the longitudinal direction of the mould.

The lowering a tilting motion continues until the root end insertsubstantially contacts the moulding surface 22 of mould 20, after whicha second motion step (from FIG. 18 to FIG. 19) is carried out. In thesecond motion step, the frame 86 with mounting plate 70 and root endinsert are pivoted until the mounting plate 86 is oriented arrangedsubstantially vertically and the root end insert rests on the mouldsurface 22 of the mould 20. This motion ensures that the fibre material68 that has already been arranged on the mould surface 22 is notdistorted or otherwise wrinkled.

Afterwards, a number of inner fibre layers 95 are as shown in FIG. 20arranged on top of the root end insert. The inner fibre layers 95 mayfor instance be triaxial fibre layers comprising reinforcement fibresoriented −45 degrees, 0 degrees and 45 degrees compared to thelongitudinal direction of the blade shell and mould. This providesstrength in both the longitudinal direction and the transverse directionof the blade shell and increases the pull-out strength of the bushings74.

FIG. 21 shows a cross-section of the final layup at the root part of themould. As seen, the layup comprises bushings 74 and inserts 76 wrappedin a fibre layer 83 and sandwiched between outer fibre layers 68 andinner fibre layers 95.

Finally, a vacuum bag is sealed against the mould 20, and the mouldcavity formed between the vacuum bag and the mould 20 is evacuated,after which a liquid resin is drawn into the mould cavity andimpregnates the fibre material. Finally, the resin is cured so as formthe shell part. This shell part may then be adhered to another shellpart, e.g. along leading and trailing edge thereof, so as to form theaerodynamic shell of the wind turbine blade. The mounting plates may beremoved prior to this process. Alternatively, the mounting plates may beleft on and first be removed prior to the wind turbine blade beingmounted on a wind turbine hub.

LIST OF REFERENCE NUMERALS

-   2 wind turbine-   4 tower-   6 nacelle-   8 hub-   10 blade-   11 blade shell-   14 blade tip-   16 blade root-   20 mould-   22 mould surface-   23 blade shell-   24 fibre mats-   30 fibre mat layup system-   32 first drive roller-   34 cutting device-   36 first clamping device-   38 buffer roller-   39 buffer length-   40 second drive roller-   42 tray-   44 slots-   46 storage position/retracted position-   48 draping device-   50 fibre mat roll-   60 cart/portal-   61 telescopic portion-   62 telescopic portion-   63 frame-   64 pivot-   65 wheel/track-   66 floor-   68 outer fibre layer(s)-   70 mounting plate-   71 recess-   72 bore/hole-   73 protrusions/pins/rods-   74 bushings/fastening means-   75 central bore with inner thread-   76 insert/butterfly wedge-   77 first side of mounting plate-   78 stay bolt-   79 second side of mounting plate-   80 wedge-   81 fibre layer with non-woven fibres or randomly oriented fibres-   82 fibre band-   83 fibre layer wrapped around bushings and inserts-   85 lowering mechanism/lowering device-   86 frame-   87 front guiding roller-   88 rear guiding roller-   89 front guiding slot-   90 rear guiding slot-   91 driving means/telescopic piston cylinder-   95 inner fibre layer(s)

The invention claimed is:
 1. A fibre mat layup system for laying up andcutting fibre mats in a mould for the manufacture of a fibre-reinforcedcomposite part, wherein the fibre-reinforced composite part comprises apart for a wind turbine blade wherein the system is adapted to laying upthe fibre mat as the system is moved in a longitudinal direction alongthe mould, and wherein the system comprises: a first drive roller foradvancing the fibre mat, a cutting device for cutting the fibre mat, afirst clamping device for clamping the fibre mat, while the fibre mat isbeing cut by the cutting device, a buffer roller providing a bufferlength for the fibre mat and being arranged downstream of the firstdrive roller, the first clamping device and the cutting device, thebuffer roller being movable so as to vary the buffer length of the fibremat, and a second drive roller for advancing the fibre mat and beingarranged downstream of the buffer roller.
 2. The fibre mat layup systemaccording to claim 1, wherein the fibre mat is supplied from a fibre matroll.
 3. The fibre mat layup system according to claim 1, wherein thesystem further comprises a draping device arranged downstream of thesecond drive roller.
 4. The fibre mat layup system according to claim 3,wherein the draping device comprises one or more rollers.
 5. The fibremat layup system according to claim 3, wherein the draping devicecomprises a number of brushes.
 6. The fibre mat layup system accordingto claim 1, wherein the cutting device is a sonic knife.
 7. The fibremat layup system according to claim 1, wherein the cutting device is arotary cutter.
 8. The fibre mat layup system according to claim 1,wherein the system is adapted to lay out fibre mats having a width of atleast 20 cm.
 9. The fibre mat layup system according to claim 1, whereinthe system is adapted to lay up fibre mats with a speed of between 25m/minute and 100 m/minute.
 10. The fibre mat layup system according toclaim 1, wherein the system is adapted to slow down a movement speedthereof during the cutting of the fibre mat.
 11. The fibre mat layupsystem according to claim 1, wherein the first drive roller is arrangedsubstantially vertical above the second drive roller, and is furtherarranged substantially vertical above the first clamping device.
 12. Thefibre mat layup system according to claim 1, wherein the buffer rolleris arranged so as to be movable in a substantially horizontal direction.13. The fibre mat layup system according to claim 1, wherein the bufferroller is resiliently biased.
 14. The fibre mat layup system accordingto claim 13, wherein the buffer roller is biased by use of gas pressure.15. The fibre mat layup system according to claim 13, wherein the bufferroller is biased by use of a spring.
 16. The fibre mat layup systemaccording to claim 1, wherein the buffer roller may be locked in adisengaged position, where the buffer length is minimised.
 17. A methodof manufacturing a composite part, in particular a part for a windturbine blade, such as an aerodynamic shell part, wherein fibre mats arelaid up in a mould part in a layup procedure by use of an automatedfibre mat layup system, wherein the layup procedure comprises the stepsof: a) delivering a supply of one or more fibre mats to the fibre matlayup system; b) laying up a first length of a fibre mat onto a surfaceof the mould along a first longitudinal part of the mould by moving thefibre mat layup system in a longitudinal direction of the mould; c)clamping a first part of the fibre mat with a first clamping device; d)cutting the fibre mat at a cutting position with a cutting device; e)laying up a second length of the fibre mat, while step d) is performed,by continuing to move the fibre mat layup system along the mould, whilea buffer length arranged downstream of the first part of the fibre matis being reduced, the buffer length for the fibre mat being provided bya buffer roller, the buffer roller being positioned downstream of afirst drive roller, the first clamping device and the cutting device;and f) repeating steps a)-e) to define a plurality of laid out fibremats defining the composite part.
 18. The method according to claim 17,wherein the buffer length in step e) is reduced by varying the positionof the buffer roller.
 19. The method according to claim 18, wherein thedelivery of the one or more fibre mats in step a) involves advancing theone or more fibre mats to a position, where the one or more fibre matsextend from a first drive roller to the buffer roller arrangeddownstream of the first drive roller and further onto a second driveroller arranged downstream of the buffer roller.
 20. The methodaccording to claim 19, wherein the delivery is carried out while thebuffer roller is in a retracted position, and wherein the first driveroller advances the fibre mat until the fibre mat engages the seconddrive roller.
 21. The method according to claim 20, wherein the bufferroller subsequently is moved to an engaged position.
 22. The methodaccording to claim 20, wherein the fibre mat layup system after step e)is moved to a new start position for laying up a fibre mat, while asubsequent delivery of a supply of one or more fibre mats to the fibremat layup system fibre mat is carried out.
 23. The method according toclaim 17, wherein the fibre mat layup system during step b) is movedalong the mould at a first speed, and wherein the fibre mat layup systemin step e) is moved along the mould at a second speed being lower thanthe first speed.